Catalytic cracking of light naphtha over dual riser fcc reactor

ABSTRACT

Systems and methods for producing light olefins and aromatics from light naphtha are disclosed. The light naphtha is fed to a first catalyst riser to crack the C5 to C7 hydrocarbons in the light naphtha stream. The cracked naphtha stream is fractionated to produce a stream comprising primarily C4 to C6 hydrocarbons or a stream comprising primarily C5 to C12 hydrocarbons. When the stream comprising primarily C4 to C6 hydrocarbons is fed to the second catalyst riser, the product stream from the second riser comprises light olefins as the main product. When the stream comprising primarily C5 to C12 hydrocarbons is fed to the second riser, the product stream from the second riser comprises aromatics as the main product.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/711,414, filed Jul. 27, 2018, and U.S. Provisional Patent Application No. 62/777,038, filed Dec. 7, 2018, the entire contents of each of which are hereby incorporated by reference in their entirety.

FIELD OF INVENTION

The present invention generally relates to methods of producing light olefins and aromatic hydrocarbons. More specifically, the present invention relates to a method of producing light olefins and aromatic hydrocarbons using two fluid catalytic cracking units.

BACKGROUND OF THE INVENTION

Light olefins (C₂ and C₃ olefins) are building blocks for many chemical processes. Light olefins are used to produce polyethylene, polypropylene, ethylene oxide, ethylene chloride, propylene oxide, and acrylic acid, which, in turn, are used in a wide variety of industries such as the plastic processing, construction, textile, and automotive industries. Generally, light olefins are produced by steam cracking naphtha and dehydrogenation of paraffin.

Aromatics, such as BTX (benzene, toluene, and xylene) are used in many different areas of chemical industry, especially the plastic and polymer sectors. For instance, benzene is a precursor for producing polystyrene, phenolic resins, polycarbonate, and nylon. Toluene is used for producing polyurethane and as a gasoline component. Xylene is feedstock for producing polyester fibers and phthalic anhydride. In the petrochemical industry, benzene, toluene, and xylene are conventionally produced by catalytic reforming of naphtha.

As the demand for light olefins and aromatics has increased over the last few decades, other methods have been developed to produce light olefins and/or aromatics. Fluid catalytic cracking of light naphtha stream is capable of producing both light olefins and BTX. In this process, light olefins are cracked in a fluidized bed reactor under high reaction temperature (above 600° C.) with a relatively short residence time to overcome the endothermicity of the reactions and oligomerization of light olefins. The effluent is separated to recover light olefins and aromatics. However, the overall selectivity from light naphtha to light olefins and aromatics is limited. Undesired products from the reactor effluent are merely recycled back to the same fluid catalytic cracking unit with the same reaction conditions as the fresh feed. Therefore, the recycling step in this process produces marginal improvement of the light olefins and/or aromatics productivity while consuming a large amount of energy during the endothermic process.

Overall, while methods of producing light olefins and BTX exist, the need for improvements in this field persists in light of at least the aforementioned drawbacks for the methods.

BRIEF SUMMARY OF THE INVENTION

A solution to at least some of the above-mentioned problems associated with the production process for light olefins and aromatics has been discovered. The solution resides in a method and a system that involves processing light naphtha with two fluid catalytic cracking units in series. The effluent from the first fluid catalytic cracking unit can be fractionated to form a stream comprising primarily C₄ to C₆ hydrocarbons and/or a stream comprising primarily C₅ to C₁₂ hydrocarbons, which can be fed to the second fluid catalytic cracking unit under reaction conditions optimized for producing light olefins and/or aromatics (e.g., BTX), respectively. This can be beneficial for at least improving the overall conversion rate and productivity of light olefins and/or aromatics. Notably, the reaction conditions in the second fluid catalytic cracking unit can be optimized for converting C₄ to C₆ hydrocarbons to light olefins and/or converting C₅ to C₁₂ hydrocarbons to aromatics, resulting in improved productivity of olefins and aromatics. Therefore, the methods of the present invention provide a technical advantage over at least some of the problems associated with the currently available methods for producing light olefins and aromatics mentioned above.

Embodiments of the invention include a method of producing olefins and aromatics. The method comprises feeding a light naphtha stream to a first catalyst riser of a fluid catalytic cracking (FCC) unit. The light naphtha stream has an initial boiling point in a range 15 to 40° C. and a final boiling point (FBP) in the range 65 to 350° C. The method further comprises contacting the light naphtha stream with a first catalyst in the first catalyst riser under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of the light naphtha stream and form a first cracked stream. The method further comprises fractionating the first cracked stream to produce a plurality of streams that comprise a first stream comprising primarily C₄ to C₆ hydrocarbons. The method further still comprises flowing the first stream to a second riser of the FCC unit. The method further comprises contacting the first stream with a second catalyst in the second catalyst riser under reaction conditions sufficient to crack C₄ to C₆ hydrocarbons of the first stream to form a second cracked stream comprising C₂ to C₃ olefins. The first catalyst and the second catalyst are different and the reaction conditions in the first catalyst riser are adapted such that the yield of light olefins from C₅ to C₇ hydrocarbons is 20 to 60 wt. % and the yield of aromatics from C₅ to C₇ hydrocarbons is 3 to 20 wt. %. The method further still comprises regenerating the first catalyst and the second catalyst separately.

Embodiments of the invention include a method of producing olefins and aromatics. The method comprises feeding a light naphtha stream to a first catalyst riser of a fluid catalytic cracking (FCC) unit. The light naphtha stream has an initial boiling point in a range 15 to 40° C. and a final boiling point (FBP) in the range 65 to 350° C. The method further comprises contacting the light naphtha stream with a first catalyst in the first catalyst riser under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of the light naphtha stream and form a first cracked stream. The method further comprises fractionating the first cracked stream to produce a first stream comprising primarily C₄ to C₆ hydrocarbons, a second stream comprising primarily C₂ and C₃ olefins, a third stream comprising primarily benzene, toluene, and xylene, collectively, and a fourth stream comprising dry gas. The method further comprises flowing the first stream to a second catalyst riser of the FCC unit. The method further still comprises contacting the first stream with a second catalyst in the second catalyst riser under reaction conditions sufficient to crack C₄ to C₆ hydrocarbons of the first stream to form a second cracked stream comprising C₂ to C₄ olefins. The first catalyst and the second catalyst are different. The reaction conditions in the first catalyst riser are adapted such that the yield of light olefins from C₅ to C₇ hydrocarbons is 20 to 60 wt. % and the yield of aromatics from C₅ to C₇ hydrocarbons is 3 to 20 wt. %. The reaction conditions in the second catalyst riser are adapted such that the yield of C₂ and C₃ hydrocarbons from C₄ and C₆ hydrocarbons is 0 to 70 wt. %. The method further comprises regenerating the first catalyst and the second catalyst separately.

Embodiments of the invention include a method of producing olefins and aromatics. The method comprises feeding a light naphtha stream to a first catalyst riser of a fluid catalytic cracking (FCC) unit. The light naphtha stream has an initial boiling point in a range 15 to 40° C. and a final boiling point (FBP) in the range 65 to 350° C. The method further comprises contacting the light naphtha stream with a first catalyst in the first catalyst riser under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of the light naphtha stream and form a first cracked stream. The method further comprises fractionating the first cracked stream to produce a plurality of streams that comprises a heavy processing stream comprising primarily C₅ to C₁₂ hydrocarbons. The method further still comprises flowing the heavy processing stream to a second catalyst riser of the FCC unit. The method further comprises contacting the heavy processing stream with a second catalyst in the second catalyst riser under reaction conditions sufficient to crack C₅ to C₁₂ hydrocarbons of the heavy processing stream to form a second cracked stream comprising aromatics. The first catalyst and the second catalyst are different. The reaction conditions in the first catalyst riser are adapted such that yield of light olefins from C₅ to C₇ hydrocarbons to olefins is 20 to 60 wt. % and yield of aromatics from the C₅ to C₇ hydrocarbons to aromatics is 3 to 20 wt. %. The reaction conditions in the second catalyst riser are adapted such that yield of aromatics from C₅ to C₁₂ nonaromatic hydrocarbons is 5 to 50 wt. %. The method further still comprises regenerating the first catalyst and the second catalyst separately.

The following includes definitions of various terms and phrases used throughout this specification.

The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

The terms “wt. %”, “vol. %” or “mol. %” refer to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol. % of component.

The term “substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification, includes any measurable decrease or complete inhibition to achieve a desired result.

The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

The term “Cn+ hydrocarbon,” wherein n is a positive integer, e.g. 1, 2, 3, 4, or 5, as that term is used in the specification and/or claims, means any hydrocarbon having at least n number of carbon atom(s) per molecule.

The term “dry gas” as that term is used in the specification and/or claims, means a gas stream comprising primarily methane and hydrogen, collectively, and less than 5 wt. % of water.

The use of the words “a” or “an” when used in conjunction with the term “comprising,” “including,” “containing,” or “having” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

The process of the present invention can “comprise,” “consist essentially of,” or “consist of” particular ingredients, components, compositions, etc., disclosed throughout the specification.

The term “yield,” as that term is used in the specification and/or claims, means the percentage of actual amount of product produced over theoretical amount of product that can be produced based on stoichiometry.

The term “primarily,” as that term is used in the specification and/or claims, means greater than any of 50 wt. %, 50 mol. %, and 50 vol. %. For example, “primarily” may include 50.1 wt. % to 100 wt. % and all values and ranges there between, 50.1 mol. % to 100 mol. % and all values and ranges there between, or 50.1 vol. % to 100 vol. % and all values and ranges there between.

The term “riser,” as that term is used in the specification and/or claims, means a reactor or a reaction zone, in which fluid and solids move upward substantially concurrently. The terms “downflow reactor” and “downer,” as the terms are used in the specification and/or claims, mean a reactor or a reaction zone, in which fluid and solids move downward substantially concurrently.

Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1A shows a schematic diagram for a system of producing light olefins and aromatics optimized for high light olefins productivity, according to embodiments of the invention;

FIG. 1B shows a schematic diagram for a system of producing light olefins and aromatics optimized for high aromatics productivity, according to embodiments of the invention; and

FIG. 2 shows a schematic flowchart for a method of producing light olefins and aromatics, according to embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Currently, light naphtha can be processed to produce light olefins and/or aromatics in a single catalyst riser of a fluid catalytic cracking unit at a high reaction temperature and with a short residence time. However, the overall selectivity and productivity for the process is limited as the reaction conditions and/or the catalyst in the single catalyst riser of the fluid catalytic cracking unit cannot be optimized to convert all the components in the light naphtha to light olefins and/or aromatics. Furthermore, the recycling of all the undesirable fractions from the single fluid catalytic cracking unit consumes a large amount of energy while producing a limited additional amount of light olefins and/or aromatics. The present invention provides a solution to at least one of the problems. The solution is premised on a method including using a second fluid catalytic cracking unit to further crack the C₄ to C₆ and/or C₅ to C₁₂ hydrocarbons from the effluent of the first catalyst riser to form additional light olefins and/or aromatics with high yields, resulting in improved overall productivity and energy efficiency. These and other non-limiting aspects of the present invention are discussed in further detail in the following section.

A. System for Processing Crude Oil and Producing Olefins and Aromatics

In embodiments of the invention, the system for producing light olefins and aromatics can include a system comprising two catalyst risers of a fluid catalytic cracking unit and a fractionation unit shared by the two catalyst risers. With reference to FIG. 1A, a schematic diagram is shown of system 100 that is capable of processing a light naphtha stream to produce light olefins C₂ and C₃ olefins and aromatics with improved overall selectivity and production efficiency compared to conventional fluid catalytic cracking process. System 100 may be optimized for light olefins production. According to embodiments of the invention, system 100 includes first catalyst riser 101 of a fluid catalytic cracking (FCC) unit configured to receive and catalytically crack light naphtha stream 11 to produce first cracked stream 12. In embodiments of the invention, first cracked stream 12 may include light olefins, aromatics, dry gas, and C₄ to C₁₂ hydrocarbons. First cracked stream 12 may further include gasoline.

In embodiments of the invention, first catalyst riser 101 may include a first fluidized bed reactor. The first fluidized bed reactor may contain a first catalyst configured to catalyze the cracking reaction of light naphtha stream 11 to produce cracked stream 12. The first catalyst may include a single phase catalyst and/or multi-phase catalyst. According to embodiments of the invention, the first catalyst includes at least one component of an acidic porous zeolite. The first catalyst may be a medium pore or large pore catalyst. Non-limiting examples of the first catalyst may include Mordenite Framework Inverted (MFI), Faujasite (FAU), Mordenite (MOR), Beta, Omega structure type zeolites and combinations thereof. In embodiments of the invention, the first catalyst may include a Si/Al ratio in a range of above 20. The first catalyst may be a medium pore or large pore catalyst. The first catalyst may have a surface area in a range of 50 to 500 m²/g and all ranges and values there between including ranges of 50 to 75 m²/g, 75 to 100 m²/g, 100 to 125 m²/g, 125 to 150 m²/g, 150 to 175 m²/g, 175 to 200 m²/g, 200 to 225 m²/g, 225 to 250 m²/g, 250 to 275 m²/g, 275 to 300 m²/g, 300 to 325 m²/g, 325 to 350 m²/g, 350 to 375 m²/g, 375 to 400 m²/g, 400 to 425 m²/g, 425 to 450 m²/g, 450 to 475 m²/g, and 475 to 500 m²/g.

An outlet of first catalyst riser 101 may be in fluid communication with fractionator 102 such that first cracked stream 12 flows from first catalyst riser 101 to fractionator 102. In embodiments of the invention, fractionator 102 may include a distillation column, an acid wash unit, a base wash unit, a solvent extraction unit, or combinations thereof. According to embodiments of the invention, fractionator 102 may be configured to separate first cracked stream 12 to form first stream 15 a comprising primarily C₄ to C₆ hydrocarbons, light olefins stream 14 (a second stream), aromatic stream 16 comprising primarily BTX, and dry gas stream 13 (the fourth stream) comprising primarily methane and hydrogen, collectively and, in some embodiments, heavy stream 17 (bottom stream) comprising primarily C₁₂+ hydrocarbons. In embodiments of the invention, dry gas stream 13 may include less than 5 wt. % water.

In embodiments of the invention, a first outlet of fractionator 102 may be in fluid communication with second catalyst riser 103 of a fluid catalytic cracking unit such that first stream 15 a flows from fractionator 102 to second catalyst riser 103. According to embodiments of the invention, second catalyst riser 103 may be configured to receive and catalytically crack first stream 15 a to produce second cracked stream 18 a comprising light olefins (C₂ and C₃ olefins) and/or aromatics. In embodiments of the invention, second cracked stream 18 a may include 5 to 50 wt. % light olefins and all ranges and values there between including ranges of 5 to 10 wt. %, 10 to 15 wt. %, 15 to 20 wt. %, 20 to 25 wt. %, 25 to 30 wt. %, 30 to 35 wt. %, 35 to 40 wt. %, 40 to 45 wt. %, and 45 to 50 wt. %.

In embodiments of the invention, second catalyst riser 103 comprises a fluidized bed reactor containing a second catalyst. The second catalyst may be different from the first catalyst. Differences between the first catalyst and the second catalyst may include but are not limited to Si to Al ratio, topology (i.e., medium pore size or large pore size), surface area, promoter, post production treatment of the catalysts, and combinations thereof.

According to embodiments of the invention, an outlet of second catalyst riser 103 may be in fluid communication with an inlet of fractionator 102 such that second cracked stream 18 a flows from second riser to fractionator 102. Fractionator 102 may be further configured to separate second cracked stream 18 a to produce additional light olefins (C₂ and C₃ olefins) and/or additional aromatics (primarily BTX). In embodiments of the invention, an outlet of fractionator 102 may be in fluid communication with first catalyst riser 101 and/or second catalyst riser 103 such that heavy stream 17 (bottom stream) flows from fractionator 102 to first catalyst riser 101 and/or second catalyst riser 103.

Alternatively or additionally, as shown in FIG. 1B, fractionator may be configured to separate first cracked stream 12 to form heavy processing stream 15 b comprising primarily C₅ to C₁₂ hydrocarbons, light olefins stream 14 (a second stream), aromatic stream 16 comprising primarily BTX, and dry gas stream 13 (the fourth stream) comprising primarily methane and hydrogen, collectively and optionally heavy stream 17 comprising primarily C₁₂+ hydrocarbons. As shown in FIG. 1B, fractionator 102 may be configured to further produce light recycling stream 19 comprising primarily C₄ to C₆ hydrocarbons. An outlet of fractionator 102 may be in fluid communication with an inlet of first catalyst riser 101 such that light recycling stream 19 flows from fractionator 102 to first catalyst riser 101. According to embodiments of the invention, system 100′ as shown in FIG. 1B may be optimized for aromatics production. In system 100′ of FIG. 1B, second catalyst riser 103 may be adapted to catalytically crack heavy processing stream 15 b to produce second cracked heavy stream 18 b (cracked processing stream) comprising primarily aromatics and/or light olefins. In embodiments of the invention, second cracked heavy stream 18 b may include 5 to 60 wt. % aromatics and all ranges and values there between including ranges of 5 to 10 wt. %, 10 to 15 wt. %, 15 to 20 wt. %, 20 to 25 wt. %, 25 to 30 wt. %, 30 to 35 wt. %, 35 to 40 wt. %, 40 to 45 wt. %, 45 to 50 wt. %, 50 to 55 wt. %, and 55 to 60 wt. %. In embodiments of the invention, first catalyst riser 101 and/or second catalyst riser 103 may be replaced by a first downflow reactor and/or a second downflow reactor, respectively. Overall, configuration of system 100′ as shown in FIG. 1B is the same as system 100 as shown in FIG. 1A except the compositions of the streams (first stream 15 a and heavy stream 15 b) from fractionator 102 to second riser 103, the compositions of streams (second cracked stream 18 a and second cracked heavy stream 18 b) flowing from second riser 103 to fractionator 102, and light recycling stream 19 only in system 100′.

B. Methods of Processing Crude Oil and Producing Olefins and Aromatics

Methods of producing light olefins and aromatics have been discovered to improve the light olefins and/or aromatics yield and productivity via fluid catalytic cracking. As shown in FIG. 2, embodiments of the invention include method 200 for producing light olefins and aromatics. Method 200 may be implemented by system 100 and/or system 100′ as shown in FIG. 1A and FIG. 1B, respectively. According to embodiments of the invention, as shown in block 201, method 200 may include feeding light naphtha stream 11 to first catalyst riser 101 of a fluid catalytic cracking (FCC) unit. In embodiments of the invention, light naphtha stream has an initial boiling point (IBP) in a range of 15 to 40° C. and all ranges and values there between including ranges of 15 to 20° C., 20 to 25° C., 25 to 30° C., 30 to 35° C., and 35 to 40° C. Light naphtha stream 11 may have a final boiling point (FBP) in a range of 65 to 350° C. and all ranges and values there between including ranges of 65 to 80° C., 80 to 95° C., 95 to 110° C., 110 to 125° C., 125 to 140° C., 140 to 155° C., 155 to 170° C., 170 to 185° C., 185 to 200° C., 200 to 215° C., 215 to 230° C., 230 to 245° C., 245 to 260° C., 260 to 275° C., 275 to 290° C., 290 to 305° C., 305 to 320° C., 320 to 335° C., and 335 to 350° C.

According to embodiments of the invention, light naphtha stream 11 contains C₅ to C₇ hydrocarbons. In embodiments of the invention, method 200 further comprises contacting light naphtha stream 11 with the first catalyst in first catalyst riser 101 under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of light naphtha stream 11 and form first cracked stream 12, as shown in block 202. According to embodiments of the invention, the reaction conditions in first catalyst riser 101 at block 202 are adapted such that the yield of light olefins from C₅ to C₇ hydrocarbons is 5 to 50 wt. % and the yield of aromatics from C₅ to C₇ hydrocarbons is 5 to 30 wt. %. In embodiments of the invention, reaction conditions in first catalyst riser 101 may include a reaction temperature in a range of 600 to 720° C. and all ranges and values there between including ranges of 600 to 610° C., 610 to 620° C., 620 to 630° C., 630 to 640° C., 640 to 650° C., 650 to 660° C., 660 to 670° C., 670 to 680° C., 680 to 690° C., 690 to 700° C., 700 to 710° C., and 710 to 720° C. The reaction conditions in first catalyst riser 101 may further include a reaction pressure in a range of 14 to 73 psi and all ranges and values there between including ranges of 14 to 16 psi, 16 to 19 psi, 19 to 22 psi, 22 to 25 psi, 25 to 28 psi, 28 to 31 psi, 31 to 34 psi, 34 to 37 psi, 37 to 40 psi, 40 to 43 psi, 43 to 46 psi, 46 to 49 psi, 49 to 52 psi, 52 to 55 psi, 55 to 58 psi, 58 to 61 psi, 61 to 64 psi, 64 to 67 psi, 67 to 70 psi, and 70 to 73 psi. The weight hourly space velocity in first catalyst riser 101 may be in a range 0.5 to 30 hr⁻¹. The residence time in first catalyst riser 101 may be in a range of 1 to 10 s and all ranges and values there between including 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, and 9 s. In embodiments of the invention, the catalyst-to-oil ratio (C/O ratio) in the fluidized bed of first catalyst riser 101 may be in a range of 10 to 80 and all ranges and values there between including ranges of 10 to 15, 15 to 20, 20 to 25, 25 to 30, 30 to 35, 35 to 40, 40 to 45, 45 to 50, 50 to 55, 55 to 60, 60 to 65, 65 to 70, 70 to 75, and 75 to 80.

According to embodiments of the invention, light naphtha stream 11 may further include steam with a steam to hydrocarbon ratio of 0 to 0.5 and all ranges and values there between including ranges of 0 to 0.05, 0.05 to 0.10, 0.10 to 0.15, 0.15 to 0.20, 0.20 to 0.25, 0.25 to 0.30, 0.30 to 0.35, 0.35 to 0.40, 0.40 to 0.45, and 0.45 to 0.50. Light naphtha stream 11 may further still include dry gas comprising primarily methane and hydrogen, collectively. The dry gas may be used as a fluidization medium in first catalyst riser 101 and/or second catalyst riser 103. In embodiments of the invention, the ratio of dry gas to hydrocarbon in light naphtha stream 11 may be in a range of 0 to 0.5 and all ranges and values there between including ranges of 0 to 0.05, 0.05 to 0.10, 0.10 to 0.15, 0.15 to 0.20, 0.20 to 0.25, 0.25 to 0.30, 0.30 to 0.35, 0.35 to 0.40, 0.40 to 0.45, and 0.45 to 0.50.

In embodiments of the invention, first cracked stream 12 may include 5 to 50 wt. % light olefins and 5 to 35 wt. % aromatics (BTX). In embodiments of the invention, as shown in block 203 a, method 200 further comprises, in fractionator 102, fractionating first cracked stream 12 to produce a plurality of streams that comprises first stream 15 a comprising primarily C₄ to C₆ hydrocarbons. In embodiments of the invention, first stream 15 a comprises 50 to 100 wt. % C₄ to C₆ hydrocarbons. Alternatively or additionally, as shown in block 203 b, first cracked stream 12 may be fractionated to produce a plurality of streams including heavy processing stream 15 b instead of first stream 15 a. Heavy processing stream 15 b comprises primarily C₅ to C₁₂ hydrocarbons. Heavy processing stream 15 b may comprise 50 to 100 wt. % C₅ to C₁₂ hydrocarbons and all ranges and values there between.

According to embodiments of the invention, in both blocks 203 a and 203 b, the plurality of streams further comprises light olefin stream 14 (the second stream) comprising primarily C₂ to C₄ olefins, aromatic stream 16 (the third stream) comprising primarily BTX, and dry gas stream 13 (the fourth stream) comprising primarily methane and hydrogen, collectively, and optionally heavy stream 17 comprising primarily C₁₂+ hydrocarbons. Alternatively or additionally, at block 203 b, fractionating the first cracked stream 12 further produces light recycling stream 19 comprising primarily C₄ to C₆ hydrocarbons. Light recycling stream 19 may be flowed from fractionator 102 back to first catalyst riser 101.

According to embodiments of the invention, as shown in block 204 a, method 200 further comprises flowing first stream 15 a to second catalyst riser 103 of the FCC unit. As shown in block 205 a, method 200 may further still include contacting first stream 15 a with the second catalyst in second catalyst riser 103 under reaction conditions sufficient to crack C₄ to C₆ hydrocarbons of first stream 15 a to form second cracked stream 18 a comprising C₂ to C₄ olefins. In embodiments of the invention, second cracked stream 18 a may include 5 to 50 wt. % light olefins and all ranges and values there between including 5 to 10 wt. %, 10 to 15 wt. %, 15 to 20 wt. %, 20 to 25 wt. %, 25 to 30 wt. %, 30 to 35 wt. %, 35 to 40 wt. %, 40 to 45 wt. %, and 45 to 50 wt. %. According to embodiments of the invention, second cracked stream may further include aromatics.

According to embodiments of the invention, the reaction conditions of second catalyst riser 103 in block 205 a are adapted such that the yield of light olefins from C₄ to C₆ hydrocarbons of first stream 15 a is from 0 to 70% and the yield of aromatics from C₄ to C₆ hydrocarbons of first stream 15 a is from 5 to 30%. In embodiments of the invention, the reaction conditions at block 205 a may include a reaction temperature in a range of 500 to 700° C. and all ranges and values there between including ranges of 500 to 510° C., 500 to 510° C., 510 to 520° C., 520 to 530° C., 530 to 540° C., 540 to 550° C., 550 to 560° C., 560 to 570° C., 570 to 580° C., 580 to 590° C., 590 to 600° C., 600 to 610° C., 610 to 620° C., 620 to 630° C., 630 to 640° C., 640 to 650° C., 650 to 660° C., 660 to 670° C., 670 to 680° C., 680 to 690° C., and 690 to 700° C. The reaction conditions in block 204 may further include reaction pressure in a range of 14 to 73 psi and all ranges and values there between between including ranges of 14 to 16 psi, 16 to 19 psi, 19 to 22 psi, 22 to 25 psi, 25 to 28 psi, 28 to 31 psi, 31 to 34 psi, 34 to 37 psi, 37 to 40 psi, 40 to 43 psi, 43 to 46 psi, 46 to 49 psi, 49 to 52 psi, 52 to 55 psi, 55 to 58 psi, 58 to 61 psi, 61 to 64 psi, 64 to 67 psi, 67 to 70 psi, and 70 to 73 psi. A weight hourly space velocity in block 205 a may be in a range of 5 to 30 hr⁻¹ and all ranges and values there between including ranges of 5 to 9 hr⁻¹, 9 to 12 hr⁻¹, 12 to 15 hr⁻¹, 15 to 18 hr⁻¹, 18 to 21 hr⁻¹, 21 to 24 hr⁻¹, 24 to 27 hr⁻¹, and 27 to 30 hr⁻¹. A residence time of second catalyst riser 103 in block 204 a may be in a range of 1 to 10 s and all ranges and values there between including 2 s, 3 s, 4 s, 5 s, 6 s, 7 s, 8 s, and 9 s. The catalyst-to-oil ratio of the fluidized bed in second riser at block 205 a may be in a range of 10 to 80 and all ranges and values there between including ranges of 10 to 15, 15 to 20, 20 to 25, 25 to 30, 30 to 35, 35 to 40, 40 to 45, 45 to 50, 50 to 55, 55 to 60, 60 to 65, 65 to 70, 70 to 75, and 75 to 80. In embodiments of the invention, the second catalyst is different from the first catalyst. According to embodiments of the invention, second cracked stream 18 a is fractionated in fractionator 102 to separate additional light olefins and/or aromatics.

Alternatively or additionally, as shown in block 204 b, heavy processing stream 15 b instead of first stream 15 a may be flowed to second catalyst riser 103 of the FCC unit. As shown in block 205 b, method 200 may further include contacting heavy processing stream 15 b with the second catalyst in second catalyst riser 103 under reaction conditions sufficient to crack C₅ to C₁₂ hydrocarbons of the heavy processing stream to form second cracked heavy stream 18 b comprising aromatics. In embodiments of the invention, second cracked heavy stream 18 b may comprise 5 to 60 wt. % aromatics. In embodiments of the invention, second cracked heavy stream 18 b may further include light olefins. In embodiments of the invention, the reaction conditions in second catalyst riser 103 at block 205 b are adapted such that the yield of aromatics from C₅ to C₁₂ nonaromatic hydrocarbons is 5 to 60 wt. % and the yield of light olefins from C₅ to C₁₂ nonaromatic hydrocarbons is 5 to 30 wt. %. In embodiments of the invention, reaction conditions in second riser at block 205 b may include a reaction temperature in a range of 500 to 700° C. and all ranges and values there between. The reaction conditions in block 204 may further include reaction pressure in a range of 14 to 73 psi and all ranges and values there between. A weight hourly space velocity in block 205 b may be in a range of 0.5 to 30 hr⁻¹ and all ranges and values there between. The catalyst-to-oil ratio (C/O ratio) of the fluidized bed in second catalyst riser 103 at block 205 b may be in a range of 10 to 80 and all ranges and values there between. A residence time of second catalyst riser 103 in block 205 b may be in a range of 1 to 10 s and all ranges and values there between. In embodiments of the invention, the second catalyst in second catalyst riser 103 is different from the first catalyst in first catalyst riser 101. According to embodiments of the invention, second cracked heavy stream 18 b is fractionated in fractionator 102 to separate additional aromatics and/or light olefins.

In embodiments of the invention, method 200 may further still include regenerating the first catalyst and the second catalyst separately, as shown in block 206. Alternatively or additionally, the first catalyst and the second catalyst may be regenerated in the same regenerator. According to embodiments of the invention, the regenerating conditions may include a regeneration temperature in a range of 650 to 900° C. and all ranges and values there between including ranges of 650 to 660° C., 660 to 680° C., 680 to 700° C., 700 to 720° C., 720 to 740° C., 740 to 760° C., 760 to 780° C., 780 to 800° C., 800 to 820° C., 820 to 840° C., 840 to 860° C., 860 to 880° C., and 880 to 900° C. The regenerating at block 206 may include adding an additional stream of hydrocarbon (light or/and heavy) to maintain heat balance. According to embodiments of the invention, method 200 may include flowing a coke precursor in first catalyst riser 101 and/or second catalyst riser 103 to form coke on the first catalyst and/or second catalyst. In embodiments of the invention, the formed coke may be burnt in the regenerating at block 206 to provide heat to the first catalyst and/or second catalyst.

Although embodiments of the present invention have been described with reference to blocks of FIG. 2, it should be appreciated that operation of the present invention is not limited to the particular blocks and/or the particular order of the blocks illustrated in FIG. 2. Accordingly, embodiments of the invention may provide functionality as described herein using various blocks in a sequence different than that of FIG. 2.

As part of the disclosure of the present invention, a specific example is included below. The example is for illustrative purposes only and is not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

EXAMPLE Example 1 Production of Light Olefins and Aromatics Using Two Risers in Series Via FCC

Light straight run naphtha (LSRN) was processed in a pilot fluid catalytic cracking unit, which included two risers in series. The catalyst in both risers included ZSM-5 based catalyst. The reaction conditions in the first riser include a reaction temperature of 675° C., a reaction pressure of 38 psia, a feed flow rate of 3.96 g/min, steam flow rate of 0.1 g/min, and a catalyst-to-oil ratio (C/O ratio) of 60. The reaction conditions in the second riser included substantially the same reaction temperature, reaction pressure, feed flow rate, and steam flow rate as the first riser. The catalyst-to-oil ratio in the second riser was 61.86.

Light straight run naphtha containing primarily C₅ and C₆ hydrocarbons was fed to the first riser. All liquid products, including C₅ to C₁₂ hydrocarbons, from the first riser were mixed with light straight run naphtha at a weight ratio of 1:1. The mixture was fed to the second riser. The compositions of the effluent stream from each riser were analyzed.

TABLE 1 Compositions of the effluent streams from the first and second risers Riser 1 Riser 2 Fresh-feed 50% Fresh-Feed + 50% Recycle Temperature (C.) 675 675 Feed Rate (gr/min) 3.96 3.95 Steam Rate (gr/min) 0.10 0.11 Riser Pressure (PSIA) 38.50 38.70 C/O Ratio 60.00 61.86 Conversion 71.30 46.13 C2= + C3= 32.46 18.03 CH4 9.99 7.74 C2+ 10.37 6.89 C3+ 6.23 3.82 iC4+ 0.94 0.49 nC4+ 1.03 0.45 C4= 7.82 3.12 Coke 1.60 4.69 LCO 0.61 4.11 DCO 0.11 0.50 Total Normal Paraffin 3.39 0.28 Total Iso Paraffin 2.98 0.44 Total Normal Olefin 5.60 3.52 Total Aromatic 14.62 43.41

The results are shown in Table 1. The results show that the effluent stream from the first riser contained about 32.46 wt. % light olefins and 14.62 wt. % aromatics. The effluent stream from the second riser contained 18.03 wt. % light olefins and 43.41 wt. % aromatics. Therefore, the use of two risers in series for catalytically cracking light straight run naphtha was capable of significantly increasing the productivity of light olefins and aromatics.

In the context of the present invention, embodiments 1 through 14 are described. Embodiment 1 is a method of producing olefins and aromatics. The method includes feeding a light naphtha stream to a first catalyst riser of a fluid catalytic cracking (FCC) unit, the light naphtha stream having an initial boiling point (IBP) in a range 15 to 40° C. and a final boiling point (FBP) in a range 65 to 350° C., then contacting the light naphtha stream with a first catalyst in the first catalyst riser under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of the light naphtha stream and form a first cracked stream. The method further includes fractionating the first cracked stream to produce a plurality of streams that includes a first stream containing primarily C₄ to C₆ hydrocarbons and flowing the first stream to a second catalyst riser of the FCC unit. The method also includes contacting the first stream with a second catalyst in the second catalyst riser under reaction conditions sufficient to crack C₄ to C₆ hydrocarbons of the first stream to form a second cracked stream containing C₂ to C₃ olefins, wherein the first catalyst and the second catalyst are different and wherein the reaction conditions in the first catalyst riser are adapted such that yield of light olefins from C₅ to C₇ hydrocarbons is 20 to 60 wt. % and yield of aromatics from C₅ to C₇ hydrocarbons is 3 to 20 wt. %. In addition, the method includes regenerating the first catalyst and the second catalyst separately. Embodiment 2 is the method of embodiment 1, wherein the fractionating of the first cracked stream further produces a second stream containing primarily C₂ to C₃ olefins, a third stream containing primarily benzene, toluene, and xylene, collectively, and a fourth stream containing dry gas. Embodiment 3 is the method of embodiment 2, wherein the fractionating further produces a bottom stream containing C₁₂+ hydrocarbons. Embodiment 4 is the method of embodiment 3, wherein the bottom stream is recycled back to the first catalyst riser. Embodiment 5 is the method of any of embodiments 2 to 4, wherein the dry gas is used as fluidization medium in the first catalyst riser and/or the second catalyst riser. Embodiment 6 is the method of any of embodiments 1 to 5, wherein the reaction conditions in the second catalyst riser are adapted such that the yield of light olefins from C₄ to C₆ hydrocarbons is 0 to 90 wt. %. Embodiment 7 is the method of any of embodiments 1 to 6, wherein the first catalyst and/or the second catalyst contains an acidic porous zeolite including Mordenite Framework Inverted (MFI), Faujasite (FAU), Mordenite (MOR), Beta, Omega structure type zeolites. Embodiment 8 is the method of any of embodiments 1 to 7, wherein the first catalyst and the second catalyst are different in parameters including silicon to aluminum ratio, pore size, surface area, promotor, or combinations thereof. Embodiment 9 is the method of any of embodiments 1 to 8, wherein the reaction conditions in the first catalyst riser include a reaction temperature of 600 to 720° C., a steam to hydrocarbon ratio of 0 to 0.5, and dry gas to hydrocarbon ratio of 0 to 0.5. Embodiment 10 is the method of any of embodiments 1 to 9, wherein the reaction conditions in the second catalyst riser include a reaction temperature of 600 to 720° C., a steam to hydrocarbon ratio of 0 to 0.5, and dry gas to hydrocarbon ratio of 0 to 0.5.

Embodiment 11 is a method of producing olefins and aromatics. The method includes feeding a light naphtha stream to a first catalyst riser of a fluid catalytic cracking (FCC) unit, the light naphtha stream having an initial boiling point in a range 15 to 40° C. and a final boiling point (FBP) in a range 65 to 350° C., then contacting the light naphtha stream with a first catalyst in the first catalyst riser under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of the light naphtha stream and form a first cracked stream. The method also includes fractionating the first cracked stream to produce a plurality of streams that includes a hydrocarbon processing stream containing primarily C₅ to C₁₂ hydrocarbons and flowing the hydrocarbon processing stream to a second catalyst riser of the FCC unit. Further, the method includes contacting the hydrocarbon processing stream with a second catalyst in the second catalyst riser under reaction conditions sufficient to crack C₅ to C₁₂ hydrocarbons of the hydrocarbon processing stream to form a second cracked processing stream containing aromatics, wherein the first catalyst and the second catalyst are different and wherein the reaction conditions in the first catalyst riser are adapted such that yield of light olefins from C₅ to C₇ hydrocarbons is 5 to 35 wt. % and yield of aromatics from C₅ to C₇ hydrocarbons is 5 to 50 wt. % and wherein the reaction conditions in the second catalyst rise are adapted such that yield of aromatics from C₅ to C₁₂ nonaromatic hydrocarbons is 5 to 60 wt. %, and regenerating the first catalyst and the second catalyst separately. Embodiment 12 is the method of embodiment 11, wherein the fractionating further produces a light recycling stream containing primarily C₄ to C₆ hydrocarbons, a light olefin stream containing primarily C₂ and C₃ olefins, a dry gas stream containing primarily methane and hydrogen, collectively, an aromatic stream containing primarily benzene, toluene, and xylene, collectively. Embodiment 13 is the method of embodiment 12, wherein the light recycling stream is recycled back to the first catalyst riser. Embodiment 14 is the method of any of embodiments 11 to 13, wherein the first catalyst and/or the second catalyst contains an acidic porous zeolite including Mordenite Framework Inverted (MFI), Faujasite (FAU), Mordenite (MOR), Beta, Omega structure type zeolites. Embodiment 15 is the method of any of embodiments 11 to 14, wherein the first catalyst and the second catalyst are different in parameters including silicon to aluminum ratio, pore size, surface area, promoter composition, or combinations thereof.

Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

1. A method of producing olefins and aromatics, the method comprising: feeding a light naphtha stream to a first catalyst riser of a fluid catalytic cracking (FCC) unit, the light naphtha stream having an initial boiling point (IBP) in a range 15 to 40° C. and a final boiling point (FBP) in a range 65 to 350° C.; contacting the light naphtha stream with a first catalyst in the first catalyst riser under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of the light naphtha stream and form a first cracked stream; fractionating the first cracked stream to produce a plurality of streams that comprises a first stream comprising primarily C₄ to C₆ hydrocarbons; flowing the first stream to a second catalyst riser of the FCC unit; contacting the first stream with a second catalyst in the second catalyst riser under reaction conditions sufficient to crack C₄ to C₆ hydrocarbons of the first stream to form a second cracked stream comprising C₂ to C₃ olefins, wherein the first catalyst and the second catalyst are different and wherein the reaction conditions in the first catalyst riser are adapted such that yield of light olefins from C₅ to C₇ hydrocarbons is 20 to 60 wt. % and yield of aromatics from C₅ to C₇ hydrocarbons is 3 to 20 wt. %; and regenerating the first catalyst and the second catalyst separately.
 2. The method of claim 1, wherein the fractionating of the first cracked stream further produces a second stream comprising primarily C₂ to C₃ olefins; a third stream comprising primarily benzene, toluene, and xylene, collectively; and a fourth stream comprising dry gas.
 3. The method of claim 2, wherein the fractionating further produces a bottom stream comprising C₁₂+ hydrocarbons.
 4. The method of claim 3, wherein the bottom stream is recycled back to the first catalyst riser.
 5. The method of claim 2, wherein the dry gas is used as fluidization medium in the first catalyst riser and/or the second catalyst riser.
 6. The method of claim 1, wherein the reaction conditions in the second catalyst riser are adapted such that the yield of light olefins from C₄ to C₆ hydrocarbons is 0 to 90 wt. %.
 7. The method of claim 1, wherein the first catalyst and/or the second catalyst comprises an acidic porous zeolite including Mordenite Framework Inverted (MFI), Faujasite (FAU), Mordenite (MOR), Beta, Omega structure type zeolites.
 8. The method of claim 1, wherein the first catalyst and the second catalyst are different in parameters comprising silicon to aluminum ratio, pore size, surface area, promotor, or combinations thereof.
 9. The method of claim 1, wherein the reaction conditions in the first catalyst riser include a reaction temperature of 600 to 720° C., a steam to hydrocarbon ratio of 0 to 0.5, and dry gas to hydrocarbon ratio of 0 to 0.5.
 10. The method of claim 1, wherein the reaction conditions in the second catalyst riser include a reaction temperature of 600 to 720° C., a steam to hydrocarbon ratio of 0 to 0.5, and dry gas to hydrocarbon ratio of 0 to 0.5.
 11. A method of producing olefins and aromatics, the method comprising: feeding a light naphtha stream to a first catalyst riser of a fluid catalytic cracking (FCC) unit, the light naphtha stream having an initial boiling point in a range 15 to 40° C. and a final boiling point (FBP) in a range 65 to 350° C.; contacting the light naphtha stream with a first catalyst in the first catalyst riser under reaction conditions sufficient to crack C₅ to C₇ hydrocarbons of the light naphtha stream and form a first cracked stream; fractionating the first cracked stream to produce a plurality of streams that comprises a hydrocarbon processing stream comprising primarily C₅ to C₁₂ hydrocarbons; flowing the hydrocarbon processing stream to a second catalyst riser of the FCC unit; contacting the hydrocarbon processing stream with a second catalyst in the second catalyst riser under reaction conditions sufficient to crack C₅ to C₁₂ hydrocarbons of the hydrocarbon processing stream to form a second cracked processing stream comprising aromatics, wherein the first catalyst and the second catalyst are different, and wherein the reaction conditions in the first catalyst riser are adapted such that yield of light olefins from C₅ to C₇ hydrocarbons is 5 to 35 wt. % and yield of aromatics from C₅ to C₇ hydrocarbons is 5 to 50 wt. % and wherein the reaction conditions in the second catalyst riser are adapted such that yield of aromatics from C₅ to C₁₂ nonaromatic hydrocarbons is 5 to 60 wt. %; and regenerating the first catalyst and the second catalyst separately.
 12. The method of claim 11, wherein the fractionating further produces a light recycling stream comprising primarily C₄ to C₆ hydrocarbons, a light olefin stream comprising primarily C₂ and C₃ olefins, a dry gas stream comprising primarily methane and hydrogen, collectively, an aromatic stream comprising primarily benzene, toluene, and xylene, collectively.
 13. The method of claim 12, wherein the light recycling stream is recycled back to the first catalyst riser.
 14. The method of claim 11, wherein the first catalyst and/or the second catalyst comprises an acidic porous zeolite including Mordenite Framework Inverted (MFI), Faujasite (FAU), Mordenite (MOR), Beta, Omega structure type zeolites.
 15. The method of claim 11, wherein the first catalyst and the second catalyst are different in parameters comprising silicon to aluminum ratio, pore size, surface area, promoter composition, or combinations thereof.
 16. The method of claim 12, wherein the first catalyst and the second catalyst are different in parameters comprising silicon to aluminum ratio, pore size, surface area, promoter composition, or combinations thereof.
 17. The method of claim 13, wherein the first catalyst and the second catalyst are different in parameters comprising silicon to aluminum ratio, pore size, surface area, promoter composition, or combinations thereof.
 18. The method of claim 14, wherein the first catalyst and the second catalyst are different in parameters comprising silicon to aluminum ratio, pore size, surface area, promoter composition, or combinations thereof.
 19. The method of claim 15, wherein the first catalyst and the second catalyst are different in parameters comprising silicon to aluminum ratio, pore size, surface area, promoter composition, or combinations thereof.
 20. The method of claim 2, wherein the reaction conditions in the second catalyst riser include a reaction temperature of 600 to 720° C., a steam to hydrocarbon ratio of 0 to 0.5, and dry gas to hydrocarbon ratio of 0 to 0.5. 